[FIR] Remove the TODO in FirJvmAnnotationHelper.kt

This code should not be reachable when not
in JVM. `jvmDefaultModeState` is only
accessed from the JVM checkers.

compiler/fir/checkers/checkers.jvm/src/org/jetbrains/kotlin/fir/analysis/jvm/checkers/FirJvmAnnotationHelper.kt

@@ -15,12 +15,9 @@ import org.jetbrains.kotlin.name.StandardClassIds
 
 fun <D> FirBasedSymbol<out D>.isCompiledToJvmDefault(
     session: FirSession,
-    jvmDefaultMode: JvmDefaultMode?
+    jvmDefaultMode: JvmDefaultMode
 ): Boolean where D : FirAnnotationContainer, D : FirDeclaration {
     if (getAnnotationByClassId(StandardClassIds.Annotations.JvmDefault, session) != null) return true
-
-    // jvmDefaultMode is null only on common metadata compilation
-    // TODO: it's unclear what should be returned here if jvmDefaultMode is null, KT-57079
-    return jvmDefaultMode?.forAllMethodsWithBody ?: true
+    return jvmDefaultMode.forAllMethodsWithBody
 }
 

compiler/fir/checkers/checkers.jvm/src/org/jetbrains/kotlin/fir/analysis/jvm/checkers/declaration/FirJvmDefaultChecker.kt

@@ -26,7 +26,7 @@ object FirJvmDefaultChecker : FirBasicDeclarationChecker() {
         val annotationNoCompatibility = declaration.getAnnotationByClassId(JVM_DEFAULT_NO_COMPATIBILITY_CLASS_ID, session)
         if (annotationNoCompatibility != null) {
             val source = annotationNoCompatibility.source
-            if (jvmDefaultMode?.isEnabled != true) {
+            if (!jvmDefaultMode.isEnabled) {
                 reporter.reportOn(source, FirJvmErrors.JVM_DEFAULT_IN_DECLARATION, "JvmDefaultWithoutCompatibility", context)
                 return
             }

compiler/fir/java/src/org/jetbrains/kotlin/fir/java/JvmDefaultModeContainer.kt

@@ -11,7 +11,7 @@ import org.jetbrains.kotlin.fir.FirSessionComponent
 
 class FirJvmDefaultModeComponent(val jvmDefaultMode: JvmDefaultMode) : FirSessionComponent
 
-private val FirSession.jvmDefaultModeComponent: FirJvmDefaultModeComponent? by FirSession.nullableSessionComponentAccessor()
+private val FirSession.jvmDefaultModeComponent: FirJvmDefaultModeComponent by FirSession.sessionComponentAccessor()
 
-val FirSession.jvmDefaultModeState: JvmDefaultMode?
-    get() = jvmDefaultModeComponent?.jvmDefaultMode
+val FirSession.jvmDefaultModeState: JvmDefaultMode
+    get() = jvmDefaultModeComponent.jvmDefaultMode